Moscow — Thousands of people marched through central Moscow Sunday, on the eve of Vladimir Putin's inauguration for an unprecedented third term as Russia's president, many chanting angry slogans such as "Putin out!" and "Putin is Russia's shame!"

Unlike the mostly peaceful and even good-natured mass rallies of recent months Sunday's march ended in violence and hundreds of arrests as heavily-armored, tear gas-firing riot police moved in on a contingent of protesters who were attempting to cross a bridge that police had barricaded. The independent Moscow radio station Ekho Moskvi reported that police arrested 400 people.

Police put the number of protesters at 8,000, but organizers claimed that more than 20,000 people came out to march down a major Moscow avenue in the warm spring sunshine to Bolotnaya Square, within sight of the Kremlin, where they were to hear a rock concert and speeches from key opposition leaders.

The crowd was far larger than either organizers or police had anticipated; last week authorities granted a permit for just 5,000 participants. Many had predicted that the middle class pro-democracy movement would wane following Mr. Putin's decisive electoral victory in March, and fractious opposition leaders had already begun blaming one another for the decline in public support.

But anti-Putin Muscovites, organizing themselves through Facebook and the Russian-language VKontakte rather than through opposition parties and groups, appear to have handed everybody another surprise by showing up in numbers that journalists on the scene agreed were closer to the 20,000 estimate.

"No one expected it to end like this; the police reaction was way too harsh," says Alexei Larionov, an economist who says he hasn't attended a protest since 1991. "I got hit myself. It certainly looked like the police were under orders to be really tough. I think that had a lot to do with Putin's inauguration tomorrow. They wanted to give us a clear warning. But I don't think protests will stop because of this. This will continue."

Dissent from 'managed democracy'

The wave of protests broke out in December, shattering Russia's facade of pro-Kremlin social harmony, and throwing up a new generation of political leaders whose roots are in civil society rather than the strictly-orchestrated political system of "managed democracy."

The reaction of the authorities was not to crack down with police violence, as in the past, but to sponsor a raft of political reforms designed to take some of the wind out of protester's sails. They included an easing of requirements to officially register a political party, a return to direct elections for regional governors – albeit with Kremlin "filters" to prevent surprises – and possible establishment of a public TV channel independent of state control.

"In many ways these reforms are real, and they have gone some way to revitalizing politics in this country," says Boris Kagarlitsky, a long-time left-wing activist and head of the independent Institute for Globalization and Social Movement Studies in Moscow.

Another effect of the protests was to force Putin to adopt a populist economic program, including billions of dollars worth of new social benefits and an extremely expensive pledge to rebuild and reequip Russia's armed forces
."Putin started backing off his promises immediately after the elections," says Mr. Kagarlitsky. "Now the government says it will cut social spending, raise the pension age, and proceed with an educational reform that's actually going to turn schools into commercial enterprises. We are facing the complete privatization of the social service sector in coming years, and this is going to engender enormous protests.... It's not the middle class anymore, but Putin's own political base that's going to move into opposition."

'Maddening for thinking people'

But it has been the Russian middle class – young, educated, urban professionals and business people, who make up about 15 percent of the population – who've been coming into the streets of Moscow for the past few months to shout anti-Putin slogans, but also to argue for fair elections, rule of law, and a genuine crackdown on corruption. On Sunday, police gave them a whiff of tear gas.

"The authorities are behaving in a really arrogant manner, and it's really getting maddening for thinking people," says Andrei Petrov, a student at the prestigious Institute of Foreign Relations in Moscow, which trains Russian diplomats. "Nobody wants to split the country, or cause a disaster, but laws should be the same for everybody....

"Even if we can't change the country's leadership, we can have these public protests and show we have our positions and we're going to stick to them. These protests will continue."